Touch panel and method for manufacturing touch panel

ABSTRACT

A touch panel capable of performing display and sensing along a curved surface or a touch panel that maintains high detection sensitivity even when it is curved along a curved surface is provided. A flexible display panel is placed along a curved portion included in a surface of a support. A first film layer is attached along a surface of the display panel by a bonding layer. Second to n-th film layers (n is an integer of 2 or more) are sequentially attached along a surface of the first film layer by bonding layers. A flexible touch sensor is attached along a surface of the n-th film layer by a bonding layer.

TECHNICAL FIELD

One embodiment of the present invention relates to a display device, andparticularly to a flexible display device capable of performing displayalong a curved surface. One embodiment of the present invention alsorelates to a touch panel, and particularly to a flexible touch panelcapable of being placed along a curved surface. Furthermore, oneembodiment of the present invention relates to an electronic devicehaving a display portion.

Note that one embodiment of the present invention is not limited to theabove technical field. The technical field of one embodiment of theinvention disclosed in this specification and the like relates to anobject, a method, or a manufacturing method. In addition, one embodimentof the present invention relates to a process, a machine, manufacture,or a composition of matter. Specifically, examples of the technicalfield of one embodiment of the present invention disclosed in thisspecification include a semiconductor device, a display device, alight-emitting device, a power storage device, a memory device, a methodfor driving any of them, and a method for manufacturing any of them.

BACKGROUND ART

Recent display devices are expected to be applied to a variety of usesand become diversified. For example, a smartphone and a tablet with atouch panel are being developed as portable information appliances.

Patent Document 1 discloses a flexible active matrix light-emittingdevice in which an organic EL element and a transistor serving as aswitching element are provided over a film substrate.

REFERENCE

Patent Document 1: Japanese Published Patent Application No. 2003-174153

DISCLOSURE OF INVENTION

It is expected that placing a touch panel along a curved surface of ahousing in an electronic device will provide an unprecedented functionand application for the electronic device. For this reason, what isdesirable is a touch panel in which a display device thinned to haveflexibility is provided with a function of inputting data with a fingeror the like touching a screen as a user interface.

An object of one embodiment of the present invention is to provide atouch panel capable of performing display and sensing along a curvedsurface. Another object of one embodiment of the present invention is toprovide a touch panel that maintains high detection sensitivity evenwhen it is curved along a curved surface. Another object of oneembodiment of the present invention is to provide an electronic devicecapable of performing display and sensing along a curved surface.Another object of one embodiment of the present invention is to providean electronic device in which the detection sensitivity of a touch panelis high even in a curved portion.

Another object of one embodiment of the present invention is to providea novel display device, a novel touch sensor, a novel touch panel, or anovel electronic device.

Note that the description of these objects does not disturb theexistence of other objects. In one embodiment of the present invention,there is no need to achieve all the objects. Objects other than theabove objects will be apparent from and can be derived from thedescription of the specification and the like.

One embodiment of the present invention is a method for manufacturing atouch panel, including the following steps: placing a flexible displaypanel along a curved portion included in a surface of a support;attaching a film layer along a surface of the display panel by a bondinglayer; and attaching a flexible touch sensor along a surface of the filmlayer by a bonding layer.

Another embodiment of the present invention is a method formanufacturing a touch panel, including the following steps: placing aflexible display panel along a curved portion included in a surface of asupport; attaching a first film layer along a surface of the displaypanel by a bonding layer; sequentially attaching second to n-th filmlayers (n is an integer of 2 or more) along a surface of the first filmlayer by bonding layers; and attaching a flexible touch sensor along asurface of the n-th film layer by a bonding layer.

The method preferably includes a step of sequentially attaching (n+1)thto m-th film layers (m is an integer of n+1 or more) along a surface ofthe touch sensor after the step of attaching the touch sensor.

Another embodiment of the present invention is a touch panel including adisplay panel, first to n-th film layers (n is an integer of 2 or more),and a touch sensor that are sequentially stacked. A surface of the touchpanel is a curved surface maintained even when the touch panel is notsupported by a support.

In the touch panel, it is preferred that the display panel have athickness of 1 μm to 300 μm, that the touch sensor have a thickness of 1μm to 300 μm, and that each of the first to n-th film layers have athickness of 1 μm to 300 μm.

In the touch panel, it is preferred that any adjacent two of the displaypanel, the first to n-th film layers, and the touch sensor be attachedto each other by a bonding layer, and that the bonding layer have athickness of 300 nm to 300 μm.

One embodiment of the present invention can provide a touch panelcapable of performing display and sensing along a curved surface.Another embodiment of the present invention can provide a touch panelwhose detection sensitivity is high even when it is curved along acurved surface.

Another embodiment of the present invention can provide a novel displaydevice (display panel), touch sensor, or touch panel. Note that thedescription of these effects does not disturb the existence of othereffects. One embodiment of the present invention does not necessarilyachieve all the effects. Other effects will be apparent from and can bederived from the description of the specification, the drawings, theclaims, and the like.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIGS. 1A1 and 1A2 illustrate a structure example of an electronicdevice, and FIGS. 1B and 1C illustrate a structure example of a touchpanel;

FIGS. 2A and 2B illustrate structure examples of a touch panel;

FIG. 3 illustrates a structure example of a touch panel;

FIGS. 4A1, 4A2, 4B1, 4B2, 4C1, 4C2, and 4D illustrate an example of amethod for manufacturing a touch panel;

FIGS. 5A1, 5A2, 5B1, 5B2, 5C1, and 5C2 illustrate structure examples ofan electronic device;

FIG. 6 illustrates a structure example of a touch sensor;

FIGS. 7A to 7C illustrate structure examples of a touch sensor;

FIG. 8 illustrates a structure example of a display panel;

FIG. 9 illustrates a configuration example of a circuit applicable to adisplay panel;

FIGS. 10A and 10B illustrate structure examples of a display panel;

FIG. 11 illustrates a structure example of a display panel;

FIGS. 12A and 12B illustrate structure examples of an electronic device,and FIGS. 12C to 12E illustrate structure examples of a lighting device;

FIGS. 13A to 13D illustrate structure examples of an electronic device;

FIG. 14 illustrates a stacked-layer structure in Example 3;

FIG. 15 is a photograph of a touch panel in Example 3;

FIGS. 16A and 16B are a circuit diagram and a timing chart in Example 1;

FIGS. 17A and 17B are circuit diagrams in Example 1;

FIGS. 18A and 18B show input-output characteristics in Example 1;

FIG. 19 shows results of calculating output characteristics of circuitsin Example 1;

FIG. 20A is a photograph showing a display panel in measurement and FIG.20B shows results of measuring electromagnetic noise in Example 1;

FIG. 21 is a schematic top diagram of a test element in Example 2;

FIG. 22 shows results of measuring resistance in Example 2; and

FIGS. 23A and 23B show output characteristics of a touch sensor inExample 2.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments will be described in detail with reference to the drawings.Note that the present invention is not limited to the description below,and it is easily understood by those skilled in the art that variouschanges and modifications can be made without departing from the spiritand scope of the present invention. Accordingly, the present inventionshould not be interpreted as being limited to the content of theembodiments below.

Note that in the structures of the invention described below, the sameportions or portions having similar functions are denoted by the samereference numerals in different drawings, and description of suchportions is not repeated. In some cases, the same hatching pattern isused for portions having similar functions, and the portions are notdenoted by reference numerals.

Note that in each drawing described in this specification, the size, thelayer thickness, or the region of each component is exaggerated forclarity in some cases; therefore, embodiments of the present inventionare not limited to such a scale.

Note that in this specification and the like, ordinal numbers such asfirst and second are used in order to avoid confusion among componentsand do not limit the number.

Embodiment 1

In this embodiment, a touch panel of one embodiment of the presentinvention and examples of electronic devices having the touch panel willbe described with reference to drawings.

Structure Example

FIGS. 1A1 and 1A2 are schematic perspective diagrams of an electronicdevice 10. FIG. 1A1 illustrates the front surface, right side surface,and top surface of the electronic device 10. FIG. 1A2 illustrates theback surface, left side surface, and top surface of the electronicdevice 10. Note that the side A and the side B of the line A-B in FIGS.1A1 and 1A2 are the front side and the back side of the electronicdevice 10, respectively.

The electronic device 10 is provided with a touch panel 100 capable ofdisplay on a surface of a housing 101. The touch panel 100 is positionedalong surfaces of parts of regions in the top, front, and back surfacesof the housing 101 among six faces of the top, back, front, bottom,right side, and left side surfaces. In the housing 101, at least thesurfaces where the touch panel 100 is positioned have curved portions.

FIG. 1B is a schematic cross-sectional diagram along the line A-B inFIGS. 1A1 and 1A2. A region including the surface with a curved portionof the housing 101 is cut along the line A-B.

The touch panel 100 is provided along a surface of a support 103. Thesurface of the support 103 has a curved portion. A light-transmittingexterior component 102 is provided to cover the touch panel 100. Thelight-transmitting exterior component 102 is preferably used at least ina region of the housing 101 that overlaps with a display portion of thetouch panel 100. The support 103 and the exterior component 102 may bepart of the housing 101.

The curved portion of the surface of the support 103 is preferably asurface that can be made by transforming a plane without stretching orcompressing (i.e., a developable surface).

The support 103 has a function of maintaining the shape of the touchpanel 100. For the support 103, a material with higher stiffness than atleast the touch panel 100 (e.g., resin, glass, or metal) can be used.

As the support 103, it is possible to use a support for determining theshape of the touch panel 100 in an example of manufacturing steps of thetouch panel 100 that is described later. Note that the support 103 isnot necessarily provided when it is not required in the housing 101, orthe support 103 may be part of the housing 101.

For the exterior component 102, a light-transmitting material (e.g.,glass or an organic material such as acrylic) can be used. Since asurface of the exterior component 102 serves as a touch surface, theexterior component 102 is preferably an insulator. A high dielectricconstant material is preferably used for the exterior component 102, inwhich case the detection sensitivity of the touch panel 100 can beincreased.

When a surface of the touch panel 100 functions as a touch surface, itis possible that the exterior component 102 is not provided and thesurface of the touch panel 100 is exposed. In this case, the surface ofthe touch panel 100 is preferably coated with a material having highhardness.

FIG. 1C is an enlarged schematic cross-sectional diagram of a regionsurrounded by dashed lines in FIG. 1B. FIG. 2A is a schematic diagramshowing that the components illustrated in FIG. 1C are separated fromeach other.

The touch panel 100 includes a display panel 111, a touch sensor 112,and a plurality of film layers 113. The display panel 111 and the touchsensor 112 are stacked so that the display panel 111 is placed on thesupport 103 side and the touch sensor 112 is placed on the exteriorcomponent 102 side. Furthermore, n film layers 113 (n is an integer of 2or more) are sandwiched between the display panel 111 and the touchsensor 112. Here, among the film layers sandwiched between the displaypanel 111 and the touch sensor 112, the film layer nearest to thedisplay panel 111 is referred to as a film layer 113(1), the film layernext nearest to the display panel 111 is referred to as a film layer113(2), and the film layer nearest to the touch sensor 112 is referredto as a film layer 113(n). In the following description, the term “filmlayer 113” is used when the film layers are not distinguished from eachother.

Two film layers 113 are preferably bonded to each other with a bondinglayer 114 as shown in FIG. 1C and the like. Similarly, bonding of thefilm layer 113(1) and the display panel 111 as well as bonding of thefilm layer 113(n) and the touch sensor 112 is preferably performed withbonding layers 114.

The display panel 111 is flexible and is provided along the surface ofthe support 103. The film layer 113(1) is provided along a surface ofthe display panel 111. The film layer 113(2) is provided along a surfaceof the film layer 113(1). Similarly, the film layer 113(n) is providedalong a surface of the film layer 113(n−1). The touch sensor 112 isprovided along a surface of the film layer 113(n).

The plurality of film layers 113 sandwiched between the display panel111 and the touch sensor 112 in such a manner can increase the distancebetween the display panel 111 and the touch sensor 112, therebydecreasing parasitic capacitance between a wiring or an electrodeincluded in the display panel 111 and that included in the touch sensor112. This prevents the detection sensitivity of the touch sensor 112from being decreased by adverse effects on the touch sensor 112 of noisethat occurs when the display panel 111 is driven.

As compared to the case where a spacer, which is a single component, issandwiched between the display panel 111 and the touch sensor 112 toincrease the distance therebetween, the use of the plurality of filmlayers 113 makes noise from the display panel 111 likely to be scatteredbetween the film layers 113, resulting in a reduction in the effect ofnoise on the touch sensor 112 in some cases.

The thickness of the display panel 111 ranges preferably from 1 μm to300 μm, for example, more preferably from 3 μm to 200 μm, still morepreferably from 5 μm to 100 μm. Typically, the thickness of the displaypanel 111 is preferably approximately 50 μm.

The thickness of the touch sensor 112 ranges preferably from 1 μm to 300μm, more preferably from 3 μm to 200 μm, still more preferably from 5 μmto 100 μm. Typically, the thickness of the touch sensor 112 ispreferably approximately 50 μm.

If the display panel 111 or the touch sensor 112 has a thickness of lessthan 1 μm, insufficient mechanical strength of the display panel 111 orthe touch sensor 112 contributes to damage. On the other hand, if thedisplay panel 111 or the touch sensor 112 has a thickness of more than500 μm, the flexibility decreases and stress applied to the displaypanel 111 or the touch sensor 112 increases because the differencebetween the inner diameter and outer diameter of the curved portionincreases. Thus, a substrate included in the display panel 111 or thetouch sensor 112 or a wiring, an element, or the like provided over thesubstrate might be damaged.

The thickness of the film layer 113 can be set as appropriate inaccordance with the number of layers to be stacked, the radius ofcurvature of a curved surface, or the like. Specifically, the thicknessof the film layer 113 is 300 μm or less, preferably 250 μm or less, morepreferably 200 μm or less, still more preferably 150 μm or less, yetstill more preferably 100 μm, even yet still more preferably 50 μm andis 1 μm or more, preferably 5 μm or more, more preferably 10 μm or more,still more preferably 20 μm or more. As the film layer 113 is thinner,the film layer 113 can be more easily provided along a curved surfacewith a smaller radius of curvature; however, the number of stackedlayers increases to increase the distance between the display panel 111and the touch sensor 112, which might result in a complicatedfabrication process. If the film layer 113 has a thickness of more than500 μm, a wrinkle, a crack, or the like might occur on the surface ofthe film layer 113 depending on the radius of curvature of the curvedsurface of the support 103.

The thickness of the bonding layer 114 is 300 μm or less, preferably 200μm or less, more preferably 100 μm or less, still more preferably 50 μmor less and is 300 nm or more, preferably 1 μm or more, more preferably5 μm or more, still more preferably 10 μm or more.

For the film layer 113 and the bonding layer 114, a low dielectricconstant material is preferably used. The film layer 113 formed using alow dielectric constant material can reduce the number of stacked filmlayers 113 as well as parasitic capacitance between the touch sensor 112and the display panel 111. For example, the film layer 113 and thebonding layer 114 are preferably formed using a material with adielectric constant in the range of 2.0 to 10.0, preferably 2.0 to 5.0,more preferably 2.0 to 4.5, still more preferably 2.0 to 4.0.

The material used for the film layer 113 and the bonding layer 114preferably has high visible light transmittance. It is preferable to usea material with transmittance of visible light (e.g., light in thewavelength range of 400 nm to 700 nm) of 70% or more, preferably 80% ormore, more preferably 85% or more, still more preferably 90% or more.

For the film layer 113, an insulating material with a light-transmittingproperty, for example, an organic insulating material or an inorganicinsulating material can be used. Moreover, a material used for the filmlayer 113 may be in a sheet form, have viscosity, or be obtained bydrying and solidifying a viscous material. Furthermore, the film layer113 may have a stacked-layer structure using at least two organicinsulating materials, at least two inorganic insulating materials, or acombination of an organic insulating material and an inorganicinsulating material.

Examples of a material used for the film layer 113 include polyesterresins such as polyethylene terephthalate (PET) and polyethylenenaphthalate (PEN), a polyacrylonitrile resin, a polyimide resin, apolymethyl methacrylate resin, a polycarbonate (PC) resin, apolyethersulfone (PES) resin, a polyamide resin, a cycloolefin resin, apolystyrene resin, a polyamide imide resin, and a polyvinyl chlorideresin. In particular, it is preferable to use a material with a lowthermal expansion coefficient, for example, a polyamide imide resin, apolyimide resin, or PET, which has a thermal expansion coefficient of30×10⁻⁶/K or lower. It is also possible to use a substrate in which afibrous body is impregnated with a resin (also referred to as prepreg)or a substrate whose thermal expansion coefficient is reduced by mixingan inorganic filler with an organic resin.

In the case where a fibrous body is included in the above material, ahigh-strength fiber of an organic compound or an inorganic compound isused as the fibrous body. The high-strength fiber is specifically afiber with a high tensile modulus of elasticity or a fiber with a highYoung's modulus. Typical examples include a polyvinyl alcohol-basedfiber, a polyester-based fiber, a polyamide-based fiber, apolyethylene-based fiber, an aramid-based fiber, a polyparaphenylenebenzobisoxazole fiber, a glass fiber, and a carbon fiber. As the glassfiber, glass fiber using E glass, S glass, D glass, Q glass, or the likecan be used. These fibers may be used in a state of a woven fabric or anonwoven fabric, and a structure body in which this fibrous body isimpregnated with a resin and the resin is cured may be used as aflexible substrate. The structure body including the fibrous body andthe resin is preferably used as a flexible substrate, in which case thereliability against bending and damage due to local pressure can beincreased.

For the bonding layer 114, a viscous material or a curable resin such asa heat curable resin, a photocurable resin, or a two-component curableresin can be used. For instance, an acrylic resin, a urethane resin, anepoxy resin, a silicone resin, or a resin having a siloxane bond can beused.

When the film layer 113 is formed using a viscous material, a materialfor the bonding layer 114 can be used, in which case the bonding layer114 can be omitted.

When the film layer 113 is thinner, the radius of curvature of thecurved surface of the support 103 can be reduced as described above.When the radius of curvature is large, a relatively thick film layer 113can be used.

Here, when the thickness of the film layer 113 is T and the smallestradius of curvature of the support 103 is R, the thickness of the filmlayer 113 can be set so that T/R is, for example, 0.2 or less,preferably 0.1 or less, more preferably 0.05 or less. For example, T/Ris 0.025 when the curvature radius R is 4 mm and the thickness T of thefilm layer 113 is 100 μm.

In reality, the radius of curvature of the curved film layer 113increases according to the thicknesses of the display panel 111 and thebonding layer 114; thus, the allowable thickness of the film layer 113can be larger than the aforementioned upper limit. The film layer113(1), which is placed nearest to the display panel 111, has thesmallest allowable thickness.

The plurality of film layers 113 are preferably films of the samematerial and with the same thickness for lower fabrication cost.Alternatively, the film layers 113 closer to the touch sensor 112 may bethicker.

As illustrated in FIG. 2B, a material combining the film layer 113 andthe bonding layer 114 may be used. For example, an adhesive film inwhich an adhesive bonding layer 114 is provided on at least one surfaceof the film layer 113 may be used. In this case, the film layer 113(n)closest to the touch sensor 112 or the film layer 113(1) closest to thedisplay panel 111 is preferably a film in which the bonding layer 114 isprovided on opposite sides of the film layer 113 so that it can bebonded to the touch sensor 112 or the display panel 111.

As illustrated in FIG. 3, between the touch sensor 112 and the exteriorcomponent 102, at least one film layer 113 may be provided so that eachfilm layer 113 is sandwiched between the bonding layers 114. Such a filmlayer 113 can easily adjust the distance between the touch sensor 112and the exterior component 102 serving as a touch surface, and thedetection sensitivity of the touch panel 100 can be optimized easilywithout changing the design of a circuit for driving the touch panel100.

FIG. 3 illustrates a structure where two film layers 113 are sandwichedbetween the exterior component 102 and the touch sensor 112. Here, amongthe film layers sandwiched between the exterior component 102 and thetouch sensor 112, the film layer 113 nearest to the exterior component102 is referred to as a film layer 113(m) (m is an integer of n+1 ormore), and the film layer 113 nearest to the touch sensor 112 isreferred to as a film layer 113(n+1).

Manufacturing Method Example

An example of a method for manufacturing the touch panel 100 will bedescribed with reference to FIGS. 4A1, 4A2, 4B1, 4B2, 4C1, 4C2, and 4D.

First, the support 103 is prepared. The support 103 can be used as acomponent incorporated in the housing 101 later. Alternatively, thesupport 103 serving as a mold may be used when a different support isused to mount the touch panel 100 in the housing 101 or when part of thehousing 101 is used as a support.

Then, the display panel 111 is placed to be curved along a surface ofthe support 103 (FIGS. 4A1 and 4A2). At this time, the support 103 andthe display panel 111 are preferably fixed with an adhesive, apressure-sensitive adhesive, or the like. When the touch panel 100 isdetached from the support 103 later, it is preferable to use an adhesiveor a pressure-sensitive adhesive with which separation is easilyperformed.

Next, the film layer 113 is attached along a surface of the displaypanel 111 with the bonding layer 114 (not shown) (FIGS. 4B1 and 4B2). Atthis time, to cover the entire surface of the display panel 111, thefilm layer 113 is preferably attached so that its end portion is placedoutside the display panel 111.

The step of attaching the film layer 113 in such a manner is repeatedthe number of times equal to the number of the film layers 113, wherebya stacked-layer structure of the film layers 113 can be obtained.

Then, the touch sensor 112 is attached along a surface of the film layer113 (specifically the film layer 113(n)) with the bonding layer 114 (notshown) (FIGS. 4C1 and 4C2).

When another film layer is provided along a surface of the touch sensor112 as illustrated in FIG. 3, it is provided in the same manner as thefilm layer 113.

FIG. 4D illustrates a state where the touch panel 100 is detached fromthe support 103. The form of the touch panel 100 can be maintained evenafter the touch panel 100 is detached from the support 103.

The touch panel 100 can be manufactured through these steps.

If the display panel 111, the n film layers 113, and the touch sensor112 are sequentially stacked along a flat surface to form a touch paneland the touch panel is curved along the support 103, external forceoccurs in the direction where the touch sensor 112, which is the mostdistant from the support 103, is particularly pulled along the curve;thus, the touch sensor 112 might be damaged.

In contrast, by using the method of sequentially providing the displaypanel 111, the n film layers 113, and the touch sensor 112 on thesurface of the support 103, stress applied to the display panel 111 andthe touch sensor 112 when they are curved is reduced, and a substrateincluded in the display panel 111 or the touch sensor 112 or a wiring,an element, and the like provided over the substrate can be preventedfrom being damaged. Thus, the highly reliable touch panel 100 can beprovided.

When the display panel 111, the film layers 113, and the touch sensor112 are curved along the curved surface, stress applied to themincreases depending on their thickness. However, the thickness of eachof the display panel 111, the n film layers 113, and the touch sensor112 is sufficiently small, so that no defect is caused by stress due totheir thickness.

If a flat-plate touch panel is curved, the touch panel cannot maintainthe curved form without a support and returns to a flat-plate shape. Incontrast, the curved shape of the touch panel 100 fabricated accordingto this manufacturing method example can be maintained even when thetouch panel 100 is detached from the support 103 (is not supported bythe support 103) as illustrated in FIG. 4D.

If a flat-plate touch panel is curved and fixed to a support, stress isapplied to the touch panel all the time, which might decrease long-termreliability. In contrast, the touch panel 100 fabricated with thismanufacturing method example maintains its curved form, so thatunintentional stress is not applied to the touch panel 100 and the touchpanel 100 with high reliability can be obtained as a result.

When this manufacturing method example is used, the number of filmlayers 113 stacked to increase the distance between the display panel111 and the touch sensor 112 is unlimited, and the touch panel can keepits curved form without problems even in the case where the number ofstacked film layers 113 is extremely large and the distance between thedisplay panel 111 and the touch sensor 112 increases. In contrast, inthe case where a flat-plate touch panel is curved, the touch sensor 112is damaged even when the distance between the display panel 111 and thetouch sensor 112 is large.

By using this manufacturing method example, stress applied to thedisplay panel 111, the touch sensor 112, and the like due to bending canbe extremely small, so that the allowable radius of curvature at thetime of bending the touch panel 100 can be extremely small. Furthermore,the distance between the display panel 111 and the touch sensor 112 canbe sufficiently large when the touch panel 100 is bent with a smallradius of curvature, resulting in higher detection sensitivity of thetouch panel 100.

In the above description, the display surface (the side where the touchsensor 112 is provided) of the touch panel 100 has a convex curve;alternatively, the display surface can have a concave surface.

[Electronic Devices]

FIGS. 5A1, 5A2, 5B1, 5B2, 5C1, and 5C2 illustrate examples of anelectronic device in which the position of the touch panel 100 isdifferent from that in FIGS. 1A1 and 1A2. In FIGS. 5A1 and 5A2, thetouch panel 100 is provided over most of the back surface of the housing101. In FIGS. 5B1 and 5B2, the touch panel 100 extends from the rightside surface to the left side surface across the front surface. In FIGS.5C1 and 5C2, the touch panel 100 extends from the back surface to theback surface across the right side surface, front surface, and left sidesurface.

Without limitation to the above structures, the electronic device can beconfigured so that the touch panel 100 is provided along a curvedsurface of the housing in various different manners. Although thesurface of the housing is convex in the above examples, the surface maybe concave or may have a shape including both a convex and a concave,such as a wave shape.

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

Embodiment 2

This embodiment will explain examples of a touch sensor and a displaypanel used in the touch panel of one embodiment of the presentinvention.

[Touch Sensor]

FIG. 6 is a schematic perspective diagram of the touch sensor 112. FIGS.7A to 7C are schematic cross-sectional diagrams along lines C-D and E-Fin FIG. 6.

As the touch sensor 112, a capacitive touch sensor can be used, forexample. Examples of a capacitive touch sensor are a surface capacitivetouch sensor and a projected capacitive touch sensor. Examples of aprojected capacitive touch sensor are a self-capacitive touch sensor anda mutual capacitive touch sensor, which differ mainly in the drivingmethod. The use of a mutual capacitive touch sensor is preferablebecause multiple points can be sensed simultaneously. An example ofusing a projected capacitive touch sensor will be described below.

The touch sensor 112 includes a plurality of electrodes 221 and aplurality of electrodes 222 between a flexible substrate 201 and aflexible substrate 202. The electrode 221 is electrically connected toone of a plurality of wirings 211. The electrode 222 is electricallyconnected to one of a plurality of wirings 212. The wirings 211 and 212are extended to the periphery of the substrate 201 and electricallyconnected to a flexible printed circuit (FPC) 205.

The electrode 221 has a shape extending in one direction. Each of theelectrodes 222 is provided between two electrodes 221. Two electrodes222 between which the electrode 221 is placed are electrically connectedto each other by a wiring 223 that intersects with the electrode 221. Adielectric layer 224 is provided between the wiring 223 and theelectrode 221, so that a capacitor is formed. In the touch sensor 112,the plurality of electrodes 222 are electrically connected by thewirings 223 and arranged in one direction, and the plurality ofelectrodes 221 are arranged in the direction intersecting with thedirection of the electrodes 222; thus, capacitors are arranged in amatrix.

The electrode 221, the electrode 222, and the wiring 223 preferably havea light-transmitting property. As shown in FIG. 6, the electrodes 221and 222 preferably have a shape with which hardly any space is generatedtherebetween. Moreover, a dummy electrode including the same conductivefilm as the electrode 221, the electrode 222, or the wiring 223 may beprovided at the space between the electrodes 221 and 222. Reducing aspace between the electrodes 221 and 222 as much as possible in such amanner can reduce transmittance unevenness. As a result, unevenness inluminance of light transmitted through the touch sensor 112 can bereduced.

As a light-transmitting conductive material, a conductive oxide such asindium oxide, indium tin oxide, indium zinc oxide, zinc oxide, or zincoxide to which gallium is added, or graphene can be used.

The electrodes 221 and 222 and the wiring 223 can be formed in such amanner that a light-transmitting conductive material is deposited on thesubstrate 201 by sputtering and then an unnecessary portion is removedby any of various patterning techniques such as photolithography.Graphene may be formed by CVD or by application of a solution in whichgraphene oxide is dispersed and subsequent reduction of graphene oxide.

The wiring 212 is electrically connected to the electrode 222. Thewiring 212 is provided so that its surface is exposed at the peripheryof the substrate 201, and can be electrically connected to the FPC 205through a connection layer 255. Note that the wiring 211 electricallyconnected to the electrode 221 can have a similar structure.

For the wirings 211 and 212, a metal material such as aluminum, gold,platinum, silver, nickel, titanium, tungsten, chromium, molybdenum,iron, cobalt, copper, or palladium or an alloy material containing anyof these metal materials can be used.

For the connection layer 255, an anisotropic conductive film (ACF), ananisotropic conductive paste (ACP), or the like can be used.

In the cross-sectional structure example in FIG. 7A, the electrode 221and the electrode 222 are formed over an insulating layer 220. Thesubstrate 201 and the insulating layer 220 are attached to each otherwith a bonding layer 231 placed therebetween. The substrate 202 and thesubstrate 201 provided with the electrodes and the like are attached toeach other with a bonding layer 232.

The bonding layer 231 and the bonding layer 232 have alight-transmitting property. A thermosetting resin or an ultravioletcurable resin can be used; for example, an acrylic resin, a urethaneresin, an epoxy resin, or a resin having a siloxane bond can be used.

A protection layer 235 is preferably provided on a surface of thesubstrate 202. The protection layer 235 can be referred to as a ceramiccoat and has a function of protecting the surface of the substrate 202when the touch sensor 112 is operated with a finger, a stylus, or thelike. The provision of the protection layer 235 is particularlypreferred when the exterior component 102 is not provided. Theprotection layer 235 can be formed using an inorganic insulatingmaterial such as silicon oxide, aluminum oxide, yttrium oxide, oryttria-stabilized zirconia (YSZ) by sputtering, a sol-gel method, or thelike. Aerosol deposition is particularly preferably employed to form theprotection layer 235, in which case a high-density film can be formed atlow temperature and mechanical strength can be increased as a result.

The protection layer 235 is provided at least on the touch surface. FIG.7A shows the case where the protection layer 235 is provided on thesurface of the substrate 202; alternatively, the protection layer 235may be provided on a surface of the substrate 201.

It is possible that the bonding layer 231 is not provided. FIG. 7Billustrates a structure where the insulating layer 220 is provided on atop surface of the substrate 201. FIG. 7C illustrates a structure wherethe insulating layer 220 is also omitted and the electrode 221, theelectrode 222, and the like are provided over the substrate 201.

The above is the description of the touch sensor.

[Display Panel]

FIG. 8 is a schematic perspective diagram of the display panel 111.

The display panel 111 includes a display portion 491 including aplurality of pixels and a wiring 457 for supplying a signal and power tothe display portion 491. The pixel included in the display portion 491is preferably provided with a transistor and a display element. Typicalexamples of the display element include an organic EL element, a liquidcrystal element, electronic ink, electronic liquid powder, and anelectrophoretic element.

In FIG. 8, the display panel 111 includes a driver circuit 493 inaddition to the display portion 491. As the driver circuit 493, acircuit functioning as a scan line driver circuit or a signal linedriver circuit, for example, can be used.

When the driver circuit 493 serves as a scan line driver circuit, acircuit (circuit A) shown in FIG. 9 can be used. The circuit A in FIG. 9includes transistors M1 to M15. Each of the transistors preferablycontains an oxide semiconductor as a semiconductor in which a channel isformed. The transistor containing an oxide semiconductor exhibitsultralow off-state current. The use of such a transistor in the circuitcan reduce shoot-through current compared with a CMOS circuit containinglow-temperature polysilicon, and noise generated from the circuit can bereduced. Consequently, the detection sensitivity of the touch panel 100can be increased.

An FPC 495 is electrically connected to the wiring 457 in FIG. 8. Asignal and power for driving the display panel 111 can be supplied fromthe FPC 495 through the wiring 457.

FIG. 8 illustrates an example where an IC 470 is mounted on the FPC 495by COF. As the IC 470, an IC functioning as a scan line driver circuitor a signal line driver circuit can be used. Note that it is possiblethat the IC 470 is not provided when the display panel 111 includescircuits serving as a scan line driver circuit and a signal line drivercircuit and when circuits serving as a scan line driver circuit and asignal line driver circuit are externally provided and a signal fordriving the display panel 111 is input through the FPC 495.

Cross-Sectional Structure Example 1

An example of a cross-sectional structure of the display panel 111 willbe described below. Here, the display panel 111 is a light-emittingdevice using an organic EL element.

FIG. 10A is a schematic cross-sectional diagram along lines G-H, I-J,and K-L in FIG. 8. The display panel illustrated in FIG. 10A is atop-emission display panel fabricated by separately depositinglight-emitting layers of different colors.

The display panel illustrated in FIG. 10A includes the display portion491, the driver circuit 493, and the FPC 495. An organic EL element andtransistors included in the display portion 491 and the driver circuit493 are sealed with a substrate 420, a substrate 428, and a bondinglayer 407.

The display panel in FIG. 10A includes the substrate 420, a bondinglayer 422, an insulating layer 424, a transistor 455, an insulatinglayer 463, an insulating layer 465, an insulating layer 405, an organicEL element 450 (a lower electrode 401, an EL layer 402, and an upperelectrode 403), the bonding layer 407, the substrate 428, and a wiring457. The substrate 428, the bonding layer 407, and the upper electrode403 transmit visible light.

In the display portion 491 of the display panel in FIG. 10A, thetransistor 455 and the organic EL element 450 are provided over thesubstrate 420 with the bonding layer 422 and the insulating layer 424placed therebetween. The organic EL element 450 includes the lowerelectrode 401 over the insulating layer 465, the EL layer 402 over thelower electrode 401, and the upper electrode 403 over the EL layer 402.The lower electrode 401 is electrically connected to a source electrodeor a drain electrode of the transistor 455. The lower electrode 401preferably reflects visible light. An end portion of the lower electrode401 is covered with the insulating layer 405.

The driver circuit 493 includes a plurality of transistors. FIG. 10Aillustrates one of the transistors in the driver circuit 493.

The wiring 457 is electrically connected to an external input terminalthrough which a signal (e.g., a video signal, a clock signal, a startsignal, or a reset signal) or a potential from the outside istransmitted to the driver circuit 493. Here, the FPC 495 is provided asthe external input terminal as an example.

To prevent an increase in the number of fabrication steps, the wiring457 is preferably formed using the same material and the same step asthose of the electrode or the wiring in the display portion or thedriver circuit. Here, an example is described in which the wiring 457 isformed using the same material and the same step as those of the sourceand drain electrodes of the transistor.

The insulating layer 463 has an effect of suppressing diffusion ofimpurities into a semiconductor included in the transistor. As theinsulating layer 465, an insulating film having a planarization functionis preferably used to reduce surface unevenness due to the transistor.

Cross-Sectional Structure Example 2

FIG. 10B illustrates a cross-sectional structure of the display paneldifferent from the above. The display panel illustrated in FIG. 10B is abottom-emission display panel fabricated using a color filter method.

The display panel in FIG. 10B includes the substrate 420, the bondinglayer 422, the insulating layer 424, a transistor 454, the transistor455, the insulating layer 463, a coloring layer 432, the insulatinglayer 465, a conductive layer 435, an insulating layer 467, theinsulating layer 405, the organic EL element 450 (the lower electrode401, the EL layer 402, and the upper electrode 403), the bonding layer407, the substrate 428, and the wiring 457. The substrate 420, thebonding layer 422, the insulating layer 424, the insulating layer 463,the insulating layer 465, the insulating layer 467, and the lowerelectrode 401 transmit visible light.

In the display portion 491 of the display panel in FIG. 10B, theswitching transistor 454, the current control transistor 455, and theorganic EL element 450 are provided over the substrate 420 with thebonding layer 422 and the insulating layer 424 placed therebetween. Theorganic EL element 450 includes the lower electrode 401 over theinsulating layer 467, the EL layer 402 over the lower electrode 401, andthe upper electrode 403 over the EL layer 402. The lower electrode 401is electrically connected to the source electrode or the drain electrodeof the transistor 455 through the conductive layer 435. An end portionof the lower electrode 401 is covered with the insulating layer 405. Theupper electrode 403 preferably reflects visible light. The display panelincludes, over the insulating layer 463, the coloring layer 432overlapping with the organic EL element 450.

The driver circuit 493 includes a plurality of transistors. FIG. 10Billustrates two of the transistors included in the driver circuit 493.

The wiring 457 is electrically connected to an external input terminalthrough which a signal or a potential from the outside is transmitted tothe driver circuit 493. Here, the wiring 457 is formed using the samematerial and the same step as those of the conductive layer 435.

The insulating layer 463 has an effect of suppressing diffusion ofimpurities into a semiconductor included in the transistor. As theinsulating layer 465 and the insulating layer 467, an insulating filmhaving a planarization function is preferably used to reduce surfaceunevenness due to the transistors and the wirings.

Cross-Sectional Structure Example 3

FIG. 11 illustrates a cross-sectional structure of the display paneldifferent from the above. The display panel illustrated in FIG. 11 is atop-emission display panel fabricated using a color filter method.

The display panel in FIG. 11 includes the substrate 420, the bondinglayer 422, the insulating layer 424, the transistor 455, the insulatinglayer 463, the insulating layer 465, the insulating layer 405, theorganic EL element 450 (the lower electrode 401, the EL layer 402, andthe upper electrode 403), the bonding layer 407, a light-blocking layer431, the coloring layer 432, an overcoat 453, an insulating layer 226, abonding layer 426, the substrate 428, and the wiring 457. The substrate428, the bonding layer 426, the insulating layer 226, the overcoat 453,the bonding layer 407, and the upper electrode 403 transmit visiblelight.

In the structure of FIG. 11, an insulating layer 496 is provided overthe insulating layer 405. Providing the insulating layer 496 serving asa spacer over the insulating layer 405 prevents the distance between thesubstrates from being smaller than the predetermined distance.

In the display portion 491 of the display panel in FIG. 11, thetransistor 455 and the organic EL element 450 are provided over thesubstrate 420 with the bonding layer 422 and the insulating layer 424placed therebetween. The organic EL element 450 includes the lowerelectrode 401 over the insulating layer 465, the EL layer 402 over thelower electrode 401, and the upper electrode 403 over the EL layer 402.The lower electrode 401 is electrically connected to the sourceelectrode or the drain electrode of the transistor 455. An end portionof the lower electrode 401 is covered with the insulating layer 405. Thelower electrode 401 preferably reflects visible light. Moreover, thedisplay panel includes the coloring layer 432 overlapping with theorganic EL element 450 with the bonding layer 407 therebetween, and thelight-blocking layer 431 overlapping with the insulating layer 405 withthe bonding layer 407 therebetween.

The driver circuit 493 includes a plurality of transistors. FIG. 11illustrates one of the transistors in the driver circuit 493.

The wiring 457 is electrically connected to an external input terminalthrough which a signal or a potential from the outside is transmitted tothe driver circuit 493. Here, as an example, the FPC 495 is provided asthe external input terminal, and the wiring 457 is formed using the samematerial and the same step as those of the source and drain electrodesof the transistor 455. A connector 497 over the insulating layer 226 isconnected to the wiring 457 through an opening provided in theinsulating layer 226, the overcoat 453, the bonding layer 407, theinsulating layer 465, and the insulating layer 463. The connector 497 isconnected to the FPC 495. The FPC 495 and the wiring 457 areelectrically connected through the connector 497.

Manufacturing Method Example

Here, a method for manufacturing a flexible touch sensor or a flexibledisplay panel will be described.

Here, a component including a pixel and a driver circuit or a componentincluding an optical component such as a color filter in a displaypanel, or a component including an electrode and a wiring in a touchsensor is referred to as an element layer for convenience. An elementlayer includes a display element, for example, and may also include awiring electrically connected to the display element and an element usedin a pixel or a circuit, such as a transistor.

Furthermore, a support provided with an insulating surface where anelement layer is formed is referred to as a base.

As a method for forming an element layer over a flexible base, there area method in which an element layer is formed directly on a base; and amethod in which an element layer is formed over a supporting base thatis different a base and has stiffness, and then the element layer isseparated from the supporting base and transferred to the base.

When the material of the base can withstand heating temperature in theprocess for forming the element layer, the element layer is preferablyformed directly on the base, in which case the manufacturing process canbe simplified. At this time, the element layer is preferably formed in astate where the base is fixed to the supporting base, in which casetransfer of the element layer in an apparatus and between apparatusescan be easy.

In the case of employing the method in which the element layer is formedover the supporting base and then transferred to the base, first, aseparation layer and an insulating layer are stacked over the supportingbase, and then the element layer is formed over the insulating layer.Then, the element layer is separated from the supporting base and thentransferred to the base. In this case, materials are selected so thatseparation occurs at the interface between the supporting base and theseparation layer, at the interface between the separation layer and theinsulating layer, or in the separation layer. With such a method, theelement layer can be formed at temperatures higher than the uppertemperature limit of the base, which improves the reliability.

It is preferred that the separation layer have a stacked-layer structureusing a layer containing a high-melting-point metal material (e.g.,tungsten) and a layer containing an oxide of the metal material, and alayer in which a plurality of layers such as a silicon nitride layer anda silicon oxynitride layer are stacked be formed over the separationlayer as the insulating layer. By using a high-melting-point metalmaterial, a high-temperature process can be performed to form theelement layer, resulting in high reliability. Impurities contained inthe element layer can be further reduced, and the crystallinity of asemiconductor or the like included in the element layer can be furtherincreased.

Examples of the separation include peeling off by application ofmechanical power, removal of the separation layer by etching, orseparation by dripping of a liquid into part of the separation interfaceto penetrate the entire separation interface. Alternatively, theseparation may be performed by heating the separation interface byutilizing a difference in coefficient of thermal expansion.

The separation layer is not necessary when separation can be performedat the interface between the supporting base and the insulating layer.For example, it is possible that glass is used as the supporting base,an organic resin such as polyimide is used for the insulating layer, astarting point of separation is set by locally heating the organic resinwith laser light or the like, and separation is performed at theinterface between the glass and the insulating layer. Alternatively, itis possible that a layer containing a material with high thermalconductivity (e.g., a metal or a semiconductor) is provided between thesupporting base and the insulating layer containing an organic resin,and this layer is heated by current so that separation easily occurs,and then separation is performed. In this case, the insulating layercontaining an organic resin can also be used as the base.

Examples of a material of the flexible base include polyester resinssuch as polyethylene terephthalate (PET) and polyethylene naphthalate(PEN), a polyacrylonitrile resin, a polyimide resin, a polymethylmethacrylate resin, a polycarbonate (PC) resin, a polyethersulfone (PES)resin, polytetrafluoroethylene (PTFE), a polyamide resin, a cycloolefinresin, a polystyrene resin, a polyamide imide resin, and a polyvinylchloride resin. In particular, it is preferable to use a material with alow thermal expansion coefficient, for example, a polyamide imide resin,a polyimide resin, or PET, which has a thermal expansion coefficient of30×10⁻⁶/K or lower. It is also possible to use a substrate in which afibrous body is impregnated with a resin (also referred to as prepreg)or a substrate whose thermal expansion coefficient is reduced by mixingan inorganic filler with an organic resin.

In the case where a fibrous body is included in the above material, ahigh-strength fiber of an organic compound or an inorganic compound isused as the fibrous body. The high-strength fiber is specifically afiber with a high tensile modulus of elasticity or a fiber with a highYoung's modulus. Typical examples include a polyvinyl alcohol-basedfiber, a polyester-based fiber, a polyamide-based fiber, apolyethylene-based fiber, an aramid-based fiber, a polyparaphenylenebenzobisoxazole fiber, a glass fiber, and a carbon fiber. As the glassfiber, glass fiber using E glass, S glass, D glass, Q glass, or the likecan be used. These fibers may be used in a state of a woven fabric or anonwoven fabric, and a structure body in which this fibrous body isimpregnated with a resin and the resin is cured may be used as aflexible substrate. The structure body including the fibrous body andthe resin is preferably used as a flexible substrate, in which case thereliability against bending and damage due to local pressure can beincreased.

Examples of Materials

Next, materials and the like that can be used for the display panel willbe described. Note that the description of the components alreadydescribed in this embodiment is omitted.

As a light-emitting element, a self-luminous element can be used, and anelement whose luminance is controlled by current or voltage is includedin the category of the light-emitting element. For example, alight-emitting diode (LED), an organic EL element, or an inorganic ELelement can be used.

There is no particular limitation on the structure of the transistors inthe display panel. For example, a forward staggered transistor or aninverted staggered transistor may be used. A top-gate transistor or abottom-gate transistor may be used. There is no particular limitation ona semiconductor material used for the transistors, and for example,silicon, germanium, or an oxide semiconductor may be used.

There is no particular limitation on the state of a semiconductormaterial used for the transistors, and an amorphous semiconductor or asemiconductor having crystallinity (a microcrystalline semiconductor, apolycrystalline semiconductor, a single crystal semiconductor, or asemiconductor partly including crystal regions) may be used. Asemiconductor having crystallinity is preferably used, in which casedeterioration of the transistor characteristics can be suppressed.

Here, for the transistors, a polycrystalline semiconductor such aspolycrystalline silicon is preferably used. Polycrystalline silicon canbe formed at lower temperature than single crystal silicon and hashigher field-effect mobility and higher reliability than amorphoussilicon. The use of such a polycrystalline semiconductor in pixelsincreases the aperture ratio of the pixels. Furthermore, by using apolycrystalline semiconductor, a gate driver circuit and a source drivercircuit can be formed over a substrate where pixels are provided evenwhen the pixel density is quite high; thus, the number of componentsincluded in an electronic device can be decreased.

Furthermore, an oxide semiconductor is preferably used for thetransistor. For example, an oxide semiconductor having a wide band gapthan silicon is preferably used. A semiconductor material having a widerband gap and a lower carrier density than silicon is preferably usedbecause the off-state current of the transistor can be reduced.

For example, the oxide semiconductor preferably contains at least indium(In) or zinc (Zn). The oxide semiconductor more preferably containsIn-M-Zn-based oxide (M is a metal such as Al, Ti, Ga, Ge, Y, Zr, Sn, La,Ce, or Hf).

As the oxide semiconductor, for example, any of the following can beused: indium oxide, tin oxide, zinc oxide, In—Zn-based oxide,Sn—Zn-based oxide, Al—Zn-based oxide, Zn—Mg-based oxide, Sn—Mg-basedoxide, In—Mg-based oxide, In—Ga-based oxide, In—Ga—Zn-based oxide (alsoreferred to as IGZO), In—Al—Zn-based oxide, In—Sn—Zn-based oxide,Sn—Ga—Zn-based oxide, Al—Ga—Zn-based oxide, Sn—Al—Zn-based oxide,In—Hf—Zn-based oxide, In—Zr—Zn-based oxide, In—Ti—Zn-based oxide,In—Sc—Zn-based oxide, In—Y—Zn-based oxide, In—La—Zn-based oxide,In—Ce—Zn-based oxide, In—Pr—Zn-based oxide, In—Nd—Zn-based oxide,In—Sm—Zn-based oxide, In—Eu—Zn-based oxide, In—Gd—Zn-based oxide,In—Tb—Zn-based oxide, In—Dy—Zn-based oxide, In—Ho—Zn-based oxide,In—Er—Zn-based oxide, In—Tm—Zn-based oxide, In—Yb—Zn-based oxide,In—Lu—Zn-based oxide, In—Sn—Ga—Zn-based oxide, In—Hf—Ga—Zn-based oxide,In—Al—Ga—Zn-based oxide, In—Sn—Al—Zn-based oxide, In—Sn—Hf—Zn-basedoxide, and In—Hf—Al—Zn-based oxide.

Here, an In—Ga—Zn-based oxide means an oxide containing In, Ga, and Znas its main components, and there is no particular limitation on theratio of In, Ga, and Zn. The In—Ga—Zn-based oxide may contain anothermetal element in addition to In, Ga, and Zn.

An oxide semiconductor film is classified roughly into a single crystaloxide semiconductor film and a non-single-crystal oxide semiconductorfilm. The non-single-crystal oxide semiconductor film includes any of ac-axis aligned crystalline oxide semiconductor (CAAC-OS) film, apolycrystalline oxide semiconductor film, a microcrystalline oxidesemiconductor film, an amorphous oxide semiconductor film, and the like.Note that the CAAC-OS film is an oxide semiconductor film including aplurality of c-axis aligned crystal parts.

As the semiconductor layer, it is particularly preferable to use anoxide semiconductor film which includes a plurality of crystal partswith c-axes aligned perpendicular to a surface where the semiconductorlayer is formed or the top surface of the semiconductor layer and inwhich the adjacent crystal parts have no grain boundary. Such an oxidesemiconductor without grain boundary prevents a crack of an oxidesemiconductor film from being caused by stress generated when a flexibledevice fabricated according to one embodiment of the present inventionis bent. Consequently, such an oxide semiconductor is preferably usedfor a flexible display device that is bent when used.

The use of such materials for the semiconductor layer makes it possibleto provide a highly reliable transistor in which a change in theelectrical characteristics is suppressed.

In addition, the low off-state current of a transistor using such anoxide semiconductor enables long-term retention of charge stored in acapacitor through the transistor. The use of such a transistor in apixel allows a driver circuit to stop while the luminance of an imagedisplayed on a display region is maintained. Thus, an electronic devicewith ultralow power consumption can be provided.

Various wirings and electrodes in a touch panel as well as a gate,source, and drain of a transistor are formed with a single-layerstructure or a stacked-layer structure using a metal such as aluminum,titanium, chromium, nickel, copper, yttrium, zirconium, molybdenum,silver, tantalum, and tungsten or an alloy containing any of thesemetals as its main component. For example, it is possible to employ asingle-layer structure of an aluminum film containing silicon; atwo-layer structure in which an aluminum film is stacked over a titaniumfilm; a two-layer structure in which an aluminum film is stacked over atungsten film; a two-layer structure in which a copper film is stackedover a copper-magnesium-aluminum alloy film; a two-layer structure inwhich a copper film is stacked over a titanium film; a two-layerstructure in which a copper film is stacked over a tungsten film; athree-layer structure in which a titanium film or a titanium nitridefilm, an aluminum film or a copper film, and a titanium film or atitanium nitride film are stacked in this order; or a three-layerstructure in which a molybdenum film or a molybdenum nitride film, analuminum film or a copper film, and a molybdenum film or a molybdenumnitride film are stacked in this order. Note that a transparentconductive material containing indium oxide, tin oxide, or zinc oxidemay be used. Copper containing manganese is preferably used because theshape controllability of etching is increased.

A light-emitting element included in the display panel includes a pairof electrodes and an EL layer between the pair of electrodes. One of thepair of electrodes functions as an anode and the other functions as acathode.

The light-emitting element may have any of a top emission structure, abottom emission structure, and a dual emission structure. A conductivefilm that transmits visible light is used as the electrode through whichlight is extracted. A conductive film that reflects visible light ispreferably used as the electrode through which light is not extracted.

A conductive film that transmits visible light can be formed using, forexample, indium oxide, indium tin oxide (ITO), indium zinc oxide, zincoxide, or zinc oxide to which gallium is added. It is also possible touse a film that is formed of a metal material such as gold, silver,platinum, magnesium, nickel, tungsten, chromium, molybdenum, iron,cobalt, copper, palladium, or titanium; an alloy containing any of thesemetal materials; or a nitride of any of these metal materials (e.g.,titanium nitride) when the film is thin enough to have alight-transmitting property. Alternatively, a stack of any of the abovematerials can be used as the conductive film. For example, a stackedfilm of ITO and an alloy of silver and magnesium is preferably used, inwhich case the conductivity can be increased. Further alternatively,graphene or the like may be used.

For the conductive film that reflects visible light, a metal materialsuch as aluminum, gold, platinum, silver, nickel, tungsten, chromium,molybdenum, iron, cobalt, copper, or palladium or an alloy containingany of these metal materials can be used, for example. Lanthanum,neodymium, germanium, or the like may be added to the metal material orthe alloy. Furthermore, an alloy containing aluminum (an aluminum alloy)such as an alloy of aluminum and titanium, an alloy of aluminum andnickel, or an alloy of aluminum and neodymium; or an alloy containingsilver such as an alloy of silver and copper, an alloy of silver,copper, and palladium, or an alloy of silver and magnesium can be usedfor the conductive film. An alloy of silver and copper is preferablebecause of its high heat resistance. When a metal film or a metal oxidefilm is stacked on an aluminum alloy film, oxidation of the aluminumalloy film can be suppressed. Examples of a material for the metal filmor the metal oxide film are titanium and titanium oxide. Alternatively,the conductive film that transmits visible light and a film containingany of the above metal materials may be stacked. For example, a stackedfilm of silver and ITO or a stacked film of an alloy of silver andmagnesium and ITO can be used.

The electrodes can be formed by an evaporation method or a sputteringmethod. Alternatively, a discharging method such as an ink-jet method, aprinting method such as a screen printing method, or a plating methodmay be used.

When a voltage higher than the threshold voltage of the light-emittingelement is applied between the lower electrode and the upper electrode,holes are injected to the EL layer from the anode side and electrons areinjected to the EL layer from the cathode side. The injected electronsand holes are recombined in the EL layer, so that a light-emittingsubstance contained in the EL layer emits light.

The EL layer includes at least a light-emitting layer. In addition tothe light-emitting layer, the EL layer may also include one or morelayers containing any of a substance with a high hole-injectionproperty, a substance with a high hole-transport property, ahole-blocking material, a substance with a high electron-transportproperty, a substance with a high electron-injection property, asubstance with a bipolar property (a substance with high electron- andhole-transport properties), and the like.

For the EL layer, either a low molecular compound or a high molecularcompound can be used, and an inorganic compound may also be used. Thelayers included in the EL layer can be formed by any of the followingmethods: an evaporation method (including a vacuum evaporation method),a transfer method, a printing method, an inkjet method, a coatingmethod, and the like.

The light-emitting element is preferably provided between a pair ofinsulating films with a high gas barrier property. Thus, impurities suchas water can be prevented from entering the light-emitting element,leading to prevention of a decrease in the reliability of the displaypanel.

Examples of the insulating layer with a high gas barrier propertyinclude a film containing nitrogen and silicon, such as a siliconnitride film or a silicon nitride oxide film, and a film containingnitrogen and aluminum, such as an aluminum nitride film. Alternatively,a silicon oxide film, a silicon oxynitride film, an aluminum oxide film,or the like may be used.

For example, the moisture vapor transmission rate of the insulating filmwith a high gas barrier property is 1×10⁻⁵ g/m²·day or less, preferably1×10⁻⁶ g/m²·day or less, more preferably 1×10⁻⁷ g/m²·day or less, stillmore preferably 1×10⁻⁸ g/m²·day or less.

A flexible material is used for the flexible substrate. For example, anorganic resin or a glass material that is thin enough to haveflexibility can be used. Furthermore, a material that transmits visiblelight is used for a substrate of the display panel from which lightemission is extracted. A metal substrate or the like may be used in thecase where the flexible substrate does not need to transmit visiblelight.

An organic resin with a lower specific gravity than glass is preferablyused for the flexible substrate, in which case the display panel can belightweight as compared to the case of using glass.

Examples of a material having flexibility and a light-transmittingproperty include polyester resins such as polyethylene terephthalate(PET) and polyethylene naphthalate (PEN), a polyacrylonitrile resin, apolyimide resin, a polymethyl methacrylate resin, a polycarbonate (PC)resin, a polyethersulfone (PES) resin, a polyamide resin, a cycloolefinresin, a polystyrene resin, a polyamide imide resin, and a polyvinylchloride resin. In particular, it is preferable to use a material with alow thermal expansion coefficient, for example, a polyamide imide resin,a polyimide resin, or PET. It is also possible to use a substrate inwhich a fibrous body is impregnated with a resin (also referred to asprepreg) or a substrate whose thermal expansion coefficient is reducedby mixing an inorganic filler with an organic resin.

In the case where a fibrous body is included in the material havingflexibility and a light-transmitting property, a high-strength fiber ofan organic compound or an inorganic compound is used as the fibrousbody. The high-strength fiber is specifically a fiber with a hightensile modulus of elasticity or a fiber with a high Young's modulus.Typical examples include a polyvinyl alcohol-based fiber, apolyester-based fiber, a polyamide-based fiber, a polyethylene-basedfiber, an aramid-based fiber, a polyparaphenylene benzobisoxazole fiber,a glass fiber, and a carbon fiber. As the glass fiber, glass fiber usingE glass, S glass, D glass, Q glass, or the like can be used. Thesefibers may be used in a state of a woven fabric or a nonwoven fabric,and a structure body in which this fibrous body is impregnated with aresin and the resin is cured may be used as a flexible substrate. Thestructure body including the fibrous body and the resin is preferablyused as a flexible substrate, in which case the reliability againstbending and damage due to local pressure can be increased.

To improve the light extraction efficiency, the refractive index of thematerial having flexibility and a light-transmitting property ispreferably high. For example, a substrate obtained by dispersing aninorganic filler having a high refractive index into an organic resincan have a higher refractive index than the substrate formed of only theorganic resin. In particular, an inorganic filler having a particlediameter as small as 40 nm or less is preferred because such a fillercan maintain optical transparency.

To obtain flexibility and bendability, the thickness of a metalsubstrate ranges preferably from 10 μm to 200 μm, more preferably from20 μm to 50 μm. Since the metal substrate has high thermal conductivity,heat generated due to light emission of a light-emitting element can beefficiently released.

There is no particular limitation on a material of the metal substrate,but it is preferable to use, for example, aluminum, copper, nickel, oran alloy such as an aluminum alloy or stainless steel.

The flexible substrate may have a structure in which a hard coat layer(e.g., a silicon nitride layer) by which a device surface is protectedfrom damage, a layer (e.g., an aramid resin layer) that can dispersepressure, or the like is stacked over a layer of any of theabove-mentioned materials. Furthermore, to suppress a decrease in thelifetime of the functional element (in particular, the organic ELelement) due to moisture and the like, an insulating film with low waterpermeability described later may be included.

The flexible substrate may be formed by stacking a plurality of layers.When a glass layer is used, barrier properties against water and oxygencan be improved and thus a reliable display panel can be provided.

For example, a flexible substrate in which a glass layer, a bondinglayer, and an organic resin layer are stacked from the side closer to anorganic EL element can be used. The thickness of the glass layer rangesfrom 20 μm to 200 μm, preferably from 25 μm to 100 μm. With such athickness, the glass layer can have both high barrier properties againstwater and oxygen and flexibility. The thickness of the organic resinlayer ranges from 10 μm to 200 μm, preferably from 20 μm to 50 μm. Byproviding such an organic resin layer on the outer side of the glasslayer, occurrence of a crack or a break in the glass layer can besuppressed and mechanical strength can be increased. With the substrateusing such a composite material of a glass material and an organicresin, a highly reliable flexible display panel can be provided.

For the bonding layer, any of a variety of curable adhesives, forexample, a light curable adhesive such as a UV curable adhesive, areactive curable adhesive, a thermal curable adhesive, and an anaerobicadhesive can be used. Examples of these adhesives include an epoxyresin, an acrylic resin, a silicone resin, a phenol resin, a polyimideresin, an imide resin, a polyvinyl chloride (PVC) resin, a polyvinylbutyral (PVB) resin, and an ethylene vinyl acetate (EVA) resin. Inparticular, a material with low moisture permeability, such as an epoxyresin, is preferred. Alternatively, a two-component-mixture-type resinmay be used. Further alternatively, an adhesive sheet or the like may beused.

Furthermore, the resin may include a drying agent. For example, asubstance that adsorbs moisture by chemical adsorption, such as oxide ofan alkaline earth metal (e.g., calcium oxide or barium oxide), can beused. Alternatively, a substance that adsorbs moisture by physicaladsorption, such as zeolite or silica gel, may be used. The drying agentis preferably included because it can prevent impurities such asmoisture from entering the functional element, thereby improving thereliability of the display panel.

It is preferable to mix a filler with a high refractive index or alight-scattering material into the resin, in which case the efficiencyof light extraction from the light-emitting element can be improved. Forexample, titanium oxide, barium oxide, zeolite, or zirconium can beused.

The above is the description of the display panel.

Note that in this specification and the like, a display element, adisplay device which is a device including a display element, alight-emitting element, and a light-emitting device which is a deviceincluding a light-emitting element can employ various modes or caninclude various elements. Examples of a display element, a displaydevice, a light-emitting element, and a light-emitting device include anelement and a device having a display medium whose contrast, luminance,reflectance, transmittance, or the like is changed by electromagneticaction, such as an EL element (e.g., an EL element including organic andinorganic materials, an organic EL element, and an inorganic ELelement), an LED (e.g., a white LED, a red LED, a green LED, and a blueLED), a transistor (a transistor that emits light depending on current),an electron emitter, a liquid crystal element, electronic ink, anelectrophoretic element, a grating light valve (GLV), a plasma displaypanel (PDP), a display element using micro electro mechanical system(MEMS), a digital micromirror device (DMD), a digital micro shutter(DMS), an interferometric modulator display (IMOD), an electrowettingelement, a MEMS shutter display element, an optical-interference-typeMEMS display element, a piezoelectric ceramic display, and a carbonnanotube. An example of a display device having EL elements is an ELdisplay. Examples of a display device including electron emitters are afield emission display (FED) and an SED-type flat panel display (SED:surface-conduction electron-emitter display). An example of a displaydevice including liquid crystal elements includes a liquid crystaldisplay (e.g., a transmissive liquid crystal display, a transflectiveliquid crystal display, a reflective liquid crystal display, adirect-view liquid crystal display, and a projection liquid crystaldisplay). An example of a display device having electronic ink,electronic liquid powder, or electrophoretic elements is electronicpaper. In a transflective liquid crystal display or a reflective liquidcrystal display, some of or all of pixel electrodes function asreflective electrodes. For example, some or all of pixel electrodes areformed to contain aluminum, silver, or the like. In such a case, amemory circuit such as SRAM can be provided under the reflectiveelectrodes, leading to lower power consumption.

In this specification and the like, it is possible to employ an activematrix method in which an active element (a non-linear element) isincluded in a pixel or a passive matrix method in which an activeelement is not included in a pixel.

In the active matrix method, as an active element, not only a transistorbut also a variety of active elements, for example, a metal insulatormetal (MIM) or a thin film diode (TFD) can be used. These elements aremanufactured with a small number of steps, resulting in lowmanufacturing cost or high yield. Furthermore, since these elements aresmall, the aperture ratio can be increased, leading to low powerconsumption and high luminance.

Since an active element is not used in a passive matrix method, thenumber of manufacturing steps is small, so that the manufacturing costcan be reduced or the yield can be improved. Furthermore, since anactive element is not used, the aperture ratio can be improved, so thatpower consumption can be reduced or higher luminance can be achieved.

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

Embodiment 3

In this embodiment, electronic devices and lighting devices that caninclude the touch panel, the touch sensor, the display panel, or thelight-emitting device of one embodiment of the present invention will bedescribed with reference to FIGS. 12A to 12E and FIGS. 13A to 13D.

Examples of electronic devices include a television set (also referredto as a television or a television receiver), a monitor of a computer orthe like, a camera such as a digital camera and a digital video camera,a digital photo frame, a mobile phone (also referred to as a cellularphone or mobile phone device), a portable game machine, a portableinformation appliance, an audio reproducing device, and a large gamemachine such as a pachinko machine.

The device manufactured according to one embodiment of the presentinvention has flexibility and therefore can be incorporated along acurved inside/outside wall surface of a house or a building or a curvedinterior/exterior surface of a car.

FIG. 12A illustrates an example of a mobile phone. A mobile phone 7400is provided with a display portion 7402 incorporated in a housing 7401,an operation button 7403, an external connection port 7404, a speaker7405, a microphone 7406, and the like. The mobile phone 7400 ismanufactured using the display device manufactured according to oneembodiment of the present invention for the display portion 7402.According to one embodiment of the present invention, a highly reliablemobile phone having a curved display portion can be provided with highyield.

When the display portion 7402 of the mobile phone 7400 in FIG. 12A istouched with a finger or the like, data can be input to the mobile phone7400. Operations such as making a call and inputting letters can beperformed by touch on the display portion 7402 with a finger or thelike.

With the operation button 7403, the power can be turned on and off.Furthermore, types of images displayed on the display portion 7402 canbe switched; for example, the image can be switched from a mail creationscreen to a main menu.

FIG. 12B illustrates an example of a wrist-watch-type portableinformation appliance. A portable information appliance 7100 includes ahousing 7101, a display portion 7102, a band 7103, a buckle 7104, anoperation button 7105, an input/output terminal 7106, and the like.

The portable information appliance 7100 is capable of executing avariety of applications such as mobile phone calls, e-mailing, readingand editing texts, music reproduction, Internet communication, and acomputer game.

The display surface of the display portion 7102 is bent, and images canbe displayed on the bent display surface. The display portion 7102includes a touch sensor, and operation can be performed by touching thescreen with a finger, a stylus, or the like. For example, an applicationcan be started by touching an icon 7107 displayed on the display portion7102.

With the operation button 7105, a variety of functions such as timesetting, power on/off, on/off control of wireless communication, settingand cancellation of manner mode, and setting and cancellation of powersaving mode can be performed. For example, the functions of theoperation button 7105 can be set freely by the operation systemincorporated in the portable information appliance 7100.

The portable information appliance 7100 can employ near fieldcommunication, which is a communication method based on an existingcommunication standard. In that case, for example, hands-free calling isachieved with mutual communication between the portable informationappliance 7100 and a headset capable of wireless communication.

Since the portable information appliance 7100 includes the input/outputterminal 7106, data can be directly transmitted to and received fromanother information appliance via a connector. Charging through theinput/output terminal 7106 is possible. Note that the charging operationmay be performed by wireless power feeding without using theinput/output terminal 7106.

The display portion 7102 of the portable information appliance 7100includes the display panel manufactured according to one embodiment ofthe present invention. According to one embodiment of the presentinvention, a highly reliable portable information appliance having acurved display portion can be provided with a high yield.

FIGS. 12C to 12E illustrate examples of lighting devices. Lightingdevices 7200, 7210, and 7220 each include a stage 7201 provided with anoperation switch 7203 and a light-emitting portion supported by thestage 7201.

The lighting device 7200 illustrated in FIG. 12C includes alight-emitting portion 7202 with a wave-shaped light-emitting surfaceand thus has an elaborate design.

A light-emitting portion 7212 included in the lighting device 7210 inFIG. 12D has two convex-curved light-emitting portions symmetricallyplaced. Thus, all directions can be illuminated with the lighting device7210 as a center.

The lighting device 7220 illustrated in FIG. 12E includes aconcave-curved light-emitting portion 7222. This is suitable forilluminating a specific range because light emitted from thelight-emitting portion 7222 is collected at the front of the lightingdevice 7220.

The light-emitting portion included in each of the lighting devices7200, 7210, and 7220 is flexible; accordingly, the light-emittingportion may be fixed on a plastic member, a movable frame, or the likeso that a light-emitting surface of the light-emitting portion can bebent freely depending on the intended use.

Although the lighting devices in which the light-emitting portion issupported by the stage are described as an example, a housing providedwith a light-emitting portion can be fixed on a ceiling or suspendedfrom a ceiling. Since the light-emitting surface can be curved, thelight-emitting surface can be bent concavely so that a particular regionis brightly illuminated, or bent convexly so that the whole room isbrightly illuminated.

When the light-emitting portion includes a touch panel, it is possibleto achieve a novel lighting device where the color of light andluminance can be changed (light can be controlled) by touch on thelight-emitting portion.

FIG. 13A is a perspective view illustrating the external shape of aportable information appliance 330. FIG. 13B is a top view of theportable information appliance 330. FIG. 13C is a perspective viewillustrating the external shape of a portable information appliance 340.

The portable information appliances 330 and 340 function as one or moreof a telephone set, an electronic notebook, and an information browsingsystem, for example. Specifically, each of the portable informationappliances 330 and 340 can be used as a smartphone.

The portable information appliances 330 and 340 can display letters andimage data on their plurality of surfaces. For example, three operationbuttons 339 can be displayed on one surface (FIGS. 13A and 13C).Furthermore, information 337 indicated by dashed rectangles can bedisplayed on another surface (FIGS. 13B and 13C). Examples of theinformation 337 include an alert for an incoming email, socialnetworking service (SNS) message, and call; the title and sender of anemail and SNS massage; the date, the time, remaining battery, and thereception strength of an antenna. On the position where the information337 is displayed, the operation button 339, an icon, or the like may bedisplayed instead of the information 337. Although FIGS. 13A and 13Bshow the example in which the information 337 is displayed at the top,one embodiment of the present invention is not limited to this example.For instance, the information 337 may be displayed on the side as in theportable information appliance 340 in FIG. 13C.

For example, a user can see the display (here, the information 337) withthe portable information appliance 330 put in a breast pocket.

Specifically, a caller's phone number, name, or the like of an incomingcall is displayed at a position that can be observed from above theportable information appliance 330. Thus, the user can see the displaywithout taking out the portable information appliance 330 from thepocket and decide whether to answer the phone.

As a display portion 333 included in a housing 335 of the portableinformation appliance 330 and a housing 336 of the portable informationappliance 340, the display device fabricated according to one embodimentof the present invention can be used. According to one embodiment of thepresent invention, a highly reliable display device having a curveddisplay portion can be provided with high yield.

As in a portable information appliance 345 illustrated in FIG. 13D,information may be displayed on at least three surfaces. Here, as anexample, information 355, information 356, and information 357 aredisplayed on different surfaces.

As a display portion 358 included in a housing 351 of the portableinformation appliance 345, the display device fabricated according toone embodiment of the present invention can be used. According to oneembodiment of the present invention, a highly reliable display devicehaving a curved display portion can be provided with high yield.

The touch panel, the touch sensor, the display panel, or thelight-emitting device of one embodiment of the present invention can beused for the display portion in the electronic device and thelight-emitting portion in the lighting device shown above. Consequently,it is possible to achieve a thin, light, and versatile electronic devicewith high detection sensitivity.

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

Example 1

[Electromagnetic Noise of Display Panel]

In this example, a display panel of one embodiment of the presentinvention was fabricated. Moreover, the results of examiningelectromagnetic noise from the display panel are shown.

As has been described, in the case where electromagnetic noise generatedwhen the display panel operates affects a touch sensor, the detectionsensitivity of the touch sensor might be decreased. For this reason,reducing electromagnetic noise caused by the display panel is effectivein increasing the detection sensitivity of the touch sensor.

One of the factors in electromagnetic noise from the display panel iselectromagnetic noise from a gate driver circuit (scan line drivercircuit). A circuit functioning as a shift register is suitable for thegate driver circuit.

Changing the waveform of an input signal such as a clock signal is aneffective way to reduce electromagnetic noise from a shift registercircuit. Specifically, as an input signal, a signal not with an idealsquare wave but with a gentle potential gradient on the rising andfalling edges is used. An input signal is preferably close to a sinewave, in which case electromagnetic noise can be further reduced.Examples of a method for generating such a waveform from a square waveinclude using a delay circuit or the like and adding a capacitor to awiring. Preferably, such a waveform may be generated by decreasing thecurrent supply capability of a signal generator circuit.

FIG. 16A illustrates a shift register circuit of one embodiment of thepresent invention. The circuit illustrated in FIG. 16A is a circuitextracted in part from the circuit in FIG. 9. Transistors M21 to M28included in the circuit of FIG. 16A are preferably transistors in whichthe above-described oxide semiconductor is contained in a channelformation region. FIG. 16B is a timing chart. When the circuit in FIG.16A is driven using input signals with waveforms shown in FIG. 16B, forexample, generation of electromagnetic noise in the circuit can beprevented. The shift register circuit of one embodiment of the presentinvention has lower shoot-through current than a shift register circuitusing a CMOS circuit described later, partly because it is composed oftransistors with the same conductivity type. If a circuit with the sameconfiguration is formed using transistors in which amorphous silicon,low-temperature polysilicon, or the like is used for a semiconductorlayer, it is necessary to add a capacitor to a node N1 to preventleakage current. As a result, current required for charging anddischarging is increased, which may increase power consumption ascompared to the case of using the oxide semiconductor.

Here, the case where a CMOS circuit in which an n-channel transistor anda p-channel are combined as shown in FIG. 17A is used in a shiftregister circuit is considered. FIG. 17B illustrates an example of ashift register circuit (circuit B) using the CMOS circuit.

The assumption is made that each transistor in FIGS. 17A and 17Bcontains silicon such as low-temperature polysilicon in a semiconductorlayer in which a channel is formed. FIG. 18A shows an example ofinput-output characteristics of the CMOS circuit in FIG. 17A. In theCMOS circuit having the transistor in which silicon is used for thesemiconductor layer, as shown in FIG. 18B, a shoot-through current flowswhen input voltage is inverted. This means that when a signal not withan ideal square wave but with a gentle potential gradient on the risingand falling edges is used as an input signal, power consumption due toshoot-through current is further increased.

Power consumption (charge consumption) of the circuit A in FIG. 9 andthat of the circuit B in FIG. 17B with varying rise time of an inputsignal were calculated for comparison. When a high-level potential atwhich the input signal is saturated is 100%, the rise time refers totime it takes for a potential level to increase from 10% to 90%.

FIG. 19 shows the calculation results. In the circuit B, powerconsumption increases as the rise time of the input signal becomeslonger. In contrast, in the circuit A, power consumption is almostconstant regardless of the length of the rise time of the input signal.

A flexible display panel using the circuit illustrated in FIG. 9 as agate driver was fabricated. The display panel was a top-emission organicEL panel using a color filter method. Transistors included in pixels andthe driver circuit of the organic EL panel were formed using CAAC-OS fora semiconductor layer. The thickness of the display panel wasapproximately 50 μm.

Electromagnetic noise emitted from the fabricated flexible display panelwas measured by a spectrum analyzer while an image was displayed. FIG.20A shows the panel at the time of measurement. The intensity ofelectromagnetic noise was measured with a spectrum analyzer probe placeddirectly above the gate driver. The measurement was performed under twoconditions: when a signal input to the gate driver has a square wave andwhen the input signal has a waveform with gentle rising. For the lattercondition, a capacitor was added to an input terminal of the displaypanel to increase the rise time of the signal from approximately 50 nsto approximately 800 ns. Although a capacitor is added in this example,addition of a resistor produces a similar effect; that is, source-sinkcurrent of a transistor for outputting a signal in an external controlcircuit for driving the organic EL panel can be reduced.

FIG. 20B shows the measurement results. As compared to the case of theinput signal with a square wave (indicated by a dashed line),electromagnetic noise emitted from the display panel was reduced in thecase where the input signal has a waveform with gentle rising (indicatedby a solid line). Furthermore, a reduction of current flowing to VDD inFIG. 9 by approximately 20% was found.

At least part of this example can be implemented in combination with anyof the embodiments described in this specification as appropriate.

Example 2

In this example, a change in resistance of a transparent conductive filmthat can be used in a touch panel and a touch sensor of one embodimentof the present invention was measured at the time of bending. Then, atouch sensor of one embodiment of the present invention was fabricated,and a change in its output signal between two states (when the touchsensor was bent and when it was not bent) was measured.

[Bending Test of Transparent Conductive Film]

FIG. 21 is a schematic top diagram of a test element fabricated toperform a bending test on the transparent conductive film. The testelement includes, over a flexible substrate, two metal wirings and atransparent electrode electrically connected to the metal wirings. Themetal wirings are electrically connected to respective ends of thetransparent electrode and an FPC. The transparent electrode has arectangular shape with a length L of 75 mm and a width W of 300 μm. Asthe transparent electrode, an indium tin oxide film containing siliconwith a thickness of approximately 230 nm was used. As the metal wiring,a tungsten film with a thickness of approximately 200 nm was used.

The bending test was performed by bending the flexible substrate in adirection parallel to the longitudinal direction of the transparentelectrode as shown in FIG. 21. The resistance of the test element wasmeasured with a varying radius of curvature of the flexible substrate.

FIG. 22 shows the measurement results. The vertical axis and thehorizontal axis of FIG. 22 represent the resistance and the inverse ofthe radius of curvature, respectively. FIG. 22 shows that the resistancedoes not change even when the radius of curvature is reduced. That is,the resistance of the transparent conductive film does not change evenwith a radius of curvature of 4 mm or less or approximately 2 mm.Accordingly, this transparent conductive film is suitably used in aflexible touch sensor, a flexible display panel, and a flexible touchpanel.

[Bending Test of Touch Sensor]

A flexible touch sensor using the above transparent conductive film as apair of electrodes was fabricated. The touch sensor was a mutualcapacitive touch sensor. The thickness of the touch sensor wasapproximately 50 μm. The transmittance of the flexible touch sensorranged from 80% to 85%.

Next, a signal output from the fabricated touch sensor was measured whenthe touch sensor was laid flat and when it was bent at 180° with aradius of curvature of 4 mm.

FIGS. 23A and 23B show the measurement results. Specifically, FIG. 23Ashows the results measured when the touch sensor is laid flat, and FIG.23B shows the results measured when the touch sensor is bent. In FIGS.23A and 23B, a solid line indicates the results obtained when an objectdoes not touch the touch sensor, and a dashed line indicates the resultsobtained when an object touches the touch sensor. The flat touch sensorand the bent touch sensor output substantially the same signals, andthis fact demonstrates that the touch sensor can operate properly ineither state.

At least part of this example can be implemented in combination with anyof the embodiments described in this specification as appropriate.

Example 3

In this example, a touch panel was manufactured with the method formanufacturing a touch panel in one embodiment of the present invention.

The touch panel was manufactured with the manufacturing method examplein Embodiment 1. FIG. 14 illustrates a stacked-layer structure of thefabricated touch panel. Here, the display panel was a top-emissionorganic EL panel using a color filter method. Transistors included inpixels and a driver circuit of the organic EL panel were formed usingCAAC-OS for a semiconductor layer. The touch sensor was a mutualcapacitive touch sensor. The display panel and the touch sensor each hada thickness of approximately 50 μm. The film layer was a PET film with athickness of approximately 50 μm. The bonding layer was a silicone resinfilm with a thickness of approximately 25 μm.

As the support, an epoxy resin having curved opposite edges with aradius of curvature of 4 mm was used. According to the manufacturingmethod described in Embodiment 1, the touch panel was fabricated alongthe opposite side surfaces and the top surface of the support.

FIG. 15 is a photograph of the fabricated touch panel. In theapplication shown in FIG. 15, text data is displayed on a region of thetop surface of the support and can be scrolled up and down by operatinga slider displayed on a region of the side surface of the support. Itwas demonstrated that multi-touch operation was achieved in the regionsat the side surface and the top surface of the support. Providing thecontrol portion at the side of the panel in this manner is convenientfor one-handed holding and operation of a mobile device.

At least part of this example can be implemented in combination with anyof the embodiments described in this specification as appropriate.

EXPLANATION OF REFERENCE

10: electronic device, 100: touch panel, 101: housing, 102: exteriorcomponent, 103: support, 111: display panel, 112: touch sensor, 113:film layer, 114: bonding layer, 201: substrate, 202: substrate, 205:FPC, 211: wiring, 212: wiring, 220: insulating layer, 221: electrode,222: electrode, 223: wiring, 224: dielectric layer, 226: insulatinglayer, 231: bonding layer, 232: bonding layer, 235: protection layer,255: connection layer, 330: portable information appliance, 333: displayportion, 335: housing, 336: housing, 337: information, 339: operationbutton, 340: portable information appliance, 345: portable informationappliance, 351: housing, 355: information, 356: information, 357:information, 358: display portion, 401: lower electrode, 402: EL layer,403: upper electrodes, 405: insulating layer, 407: bonding layer, 420:substrate, 422: bonding layer, 424: insulating layer, 426: bondinglayer, 428: substrate, 431: light-blocking layer, 432: coloring layer,435: conductive layer, 450: organic EL element, 453: overcoat, 454:transistor, 455: transistor, 457: wiring, 463: insulating layer, 465:insulating layer, 467: insulating layer, 470: IC, 491: display portion,493: driver circuit, 495: FPC, 496: insulating layer, 497: connector,7100: portable information appliance, 7101: housing, 7102: displayportion, 7103: band, 7104: buckle, 7105: operation button, 7106:input/output terminal, 7107: icon, 7200: lighting device, 7201: stage,7202: light-emitting portion, 7203: operation switch, 7210: lightingdevice, 7212: light-emitting portion, 7220: lighting device, 7222:light-emitting portion, 7400: mobile phone, 7401: housing, 7402: displayportion, 7403: operation button, 7404: external connection port, 7405:speaker, 7406: microphone

This application is based on Japanese Patent Application serial no.2013-249280 and no. 2014-104981 filed with Japan Patent Office on Dec.2, 2013 and May 21, 2014, respectively, the entire contents of which arehereby incorporated by reference.

The invention claimed is:
 1. A method for manufacturing a touch panel,comprising the steps of: placing a display panel over a support so thatthe display panel is bent along a curved surface of the support;attaching a first insulating film layer over the display panel so thatthe first insulating film layer is bent along a curved surface of thedisplay panel; attaching a second insulating film layer over the firstinsulating film layer so that the second insulating film layer is bentalong a curved surface of the first insulating film layer; and attachinga touch sensor over the second insulating film layer so that the touchsensor is bent along a curved surface of the second insulating filmlayer, wherein the display panel and the first insulating film layer areattached through a first bonding layer, wherein the first insulatingfilm layer and the second insulating film layer are attached through asecond bonding layer, and wherein at least one of the first bondinglayer and the second bonding layer comprises a light-scatteringmaterial.
 2. The method for manufacturing a touch panel, according toclaim 1, wherein each of the first bonding layer and the second bondinglayer comprises an acrylic resin, a urethane resin, an epoxy resin, asilicone resin, or a resin having a siloxane bond.
 3. The method formanufacturing a touch panel, according to claim 1, wherein the secondinsulating film layer and the touch sensor are attached through a thirdbonding layer.
 4. The method for manufacturing a touch panel, accordingto claim 3, wherein the third bonding layer comprises an acrylic resin,a urethane resin, an epoxy resin, a silicone resin, or a resin having asiloxane bond.
 5. The method for manufacturing a touch panel, accordingto claim 1, further comprising a step of attaching an exterior componentover the touch sensor so that the exterior component is bent along acurved surface of the touch sensor.
 6. The method for manufacturing atouch panel, according to claim 5, wherein the exterior component is adifferent material from the first insulating film layer and the secondinsulating film layer.
 7. The method for manufacturing a touch panel,according to claim 1, further comprising a step of detaching the displaypanel from the support.
 8. The method for manufacturing a touch panel,according to claim 1, wherein the light-scattering material is one oftitanium oxide, barium oxide, zeolite, and zirconium.
 9. A touch panelcomprising: a display panel; first to n-th insulating film layers overthe display panel, where n is an integer of 2 or more; and a touchsensor over the first to n-th insulating film layers, wherein the touchpanel comprises a curved surface, wherein the curved surface ismaintained even when the touch panel is not supported by a support,wherein any adjacent two of the display panel, the first to n-thinsulating film layers, and the touch sensor are attached to each otherby a bonding layer, and wherein the bonding layer comprises alight-scattering material.
 10. The touch panel according to claim 9,wherein the display panel has a thickness in the range of 1 μm to 300μm, wherein the touch sensor has a thickness in the range of 1 μm to 300μm, and wherein each of the first to n-th insulating film layers has athickness in the range of 1 μm to 300 μm.
 11. The touch panel accordingto claim 9, wherein the bonding layer has a thickness in the range of300 nm to 300 μm.
 12. The touch panel according to claim 9, wherein thelight-scattering material is one of titanium oxide, barium oxide,zeolite, and zirconium.